The present invention relates to a clutch adjustment method and apparatus thereof for making a steering clutch adjustment to ensure proper steering clutch performance in a tracklaying vehicle in which a right or left turn is made by controlling clutch hydraulic pressure and brake hydraulic pressure through operation of an electrical power-assisted steering lever.
In a known tracklaying vehicle such as bulldozers, the clutch and brake attached to each of the right and left drive wheels are controlled to effect right and left turns of the vehicle. More specifically, if the steering lever is operated in either the right or left steering direction during traveling of the vehicle, the clutch on the side to which the steering lever has been operated is released from its engaged state, while the brake on the same side is actuated in the braking direction with the crawler belt only on this side being brought to a stop, so that the vehicle turns in the desired direction.
The so-called electronically controlled steering systems come into common use for providing clutch and brake control. Such a steering system includes (i) an electrical power-assisted steering lever, (ii) a steering command signal generator for issuing a steering command signal in accordance with the operating amount of the steering lever and (iii) an electronic proportional control valve controlled based on the output from the steering command signal generator, and controls the clutches and brakes through control of the electronic proportional control valve.
The electronically controlled steering systems present the bothersome drawback that if variations in vehicle performance occur owing to variations in the constituents (e.g., solenoids and springs) of the control valves or variations in the thickness of the clutch disks or brake disks, mechanical adjustments (e.g., shim adjustment and stroke adjustment) have to be carried out as required whenever they occur. This steering system suffers from another problem that long use of the vehicle leads to wear etc. of the steering system including the steering brakes and steering clutches, resulting in degradation of vehicle performance.
For constantly providing desired proper steering brake or steering clutch performance to overcome the forgoing problems, it is necessary to incorporate a system which enables a brake or clutch adjustment at the time of delivery or check of a vehicle.
There is known a steering brake adjustment method carried out in the following procedure.
Step 1: A crawler belt is lifted from the ground by use of implements (blade and ripper) or jacks.
Step 2: Engine rotation is set to a low idling state.
Step 3: An adjustment mode is set.
Step 4: The crawler belt is rotated with the transmission placed in the third forward speed range (F3).
Step 5: The test starting switch is turned on. At that time, a test current flows to the brake solenoid for a specified period of time and after the elapse of the specified time, the speed of the crawler belt returns to a normal speed.
Step 6: The adjuster makes a check as to whether or not the crawler belt stopped before the speed of the crawler belt returned to the normal speed. Then, if it is determined the crawler belt stopped, the adjuster makes a check again with an increased setting of hydraulic pressure to determine whether the crawler belt stops.
Step 7: If the crawler belt did not stop before returning to the normal speed, the adjuster makes a check again with a decreased setting of hydraulic pressure to determine whether the crawler belt stops. Checks are made in this way and when the crawler belt stops, the adjustment mode is ended.
There exist no prior examples of tracklaying vehicles having the above-described electronically controlled steering system in which a steering clutch adjustment function is incorporated, and, therefore, there has been long awaited development of an adjustment system which enables desired proper steering clutch performance.
The present invention is directed to overcoming the foregoing problems and a prime object of the invention is therefore to provide a clutch adjustment method and apparatus thereof, which make it possible to adequately compensate for variations in performance as well as degradation of performance due to variations or wear in various parts.
The above object can be achieved by a clutch adjustment method according to a first aspect of the invention. The method is adapted for use with a tracklaying vehicle wherein right and left drive wheels are each provided with a clutch and a brake and wherein clutch hydraulic pressure and brake hydraulic pressure are controlled by operation of an electrical power-assisted steering lever to allow a right or left turn of the vehicle, the method being made such that when an adjustment mode is selected with the brakes in their actuated state, a command value for the clutch hydraulic pressure at the start of sliding of a clutch is detected while the clutch hydraulic pressure being gradually changed, and an adjustment for the clutch is made based on the detected command value.
According to the invention, for clutch adjustment, the adjustment mode is set with the brakes in their actuated state and clutch hydraulic pressure is gradually varied (e.g., increasing) during the adjustment mode. Then, a command value of clutch hydraulic pressure at the start of sliding of a clutch being adjusted is detected and according to this command value, a clutch adjustment is carried out. With this arrangement, variations due to different adjusters are avoided and sliding of the clutch is minimized, so that an adjustment can be automatically made to ensure adequate clutch performance. This adjustment can be carried out when no implements are mounted on the front and rear sides of the vehicle. In addition, even if sliding of the clutch being adjusted occurs, the vehicle does not move because the brakes are in their actuated state so that the clutch hydraulic pressure can be properly corrected.
According to a second aspect of the invention, there is provided a clutch adjustment apparatus adapted for use with a tracklaying vehicle wherein right and left drive wheels are each provided with a clutch and a brake and wherein clutch hydraulic pressure and brake hydraulic pressure are controlled by operation of an electrical power-assisted steering lever to allow a right or left turn of the vehicle, the apparatus comprising, as shown in the general block diagram of FIG. 1,
(a) adjustment mode setting means 1 for setting an adjustment mode for adjusting the clutch hydraulic pressure to a proper value, while the brakes being in their actuated state;
(b) clutch hydraulic pressure changing means 2 for controlling the clutch hydraulic pressure to gradually change when the adjustment mode is set by the adjustment mode setting means 1;
(c) clutch sliding start detecting means 3 for detecting a start of sliding of a clutch;
(d) clutch pressure command value detecting means 4 for detecting a clutch pressure command value at the start of sliding of the clutch, if sliding of the clutch is detected by the clutch sliding start detecting means 3 while the clutch hydraulic pressure being gradually changed by the clutch hydraulic pressure changing means 2; and
(e) clutch hydraulic pressure correcting means 5 for correcting the clutch hydraulic pressure to a proper value, based on the clutch pressure command value detected by the clutch pressure command value detecting means 4.
The second aspect of the invention is associated with an apparatus which implements the clutch adjustment method of the first aspect. For starting clutch adjustment, the adjustment mode is set by the adjustment mode setting means 1 while the brakes are in their actuated state. In this adjustment mode, the clutch hydraulic pressure is gradually changed (e.g., increasing) by the clutch hydraulic pressure changing means 2. If a start of sliding of the clutch is detected by the clutch sliding start detecting means 3 during the changing of the clutch hydraulic pressure, a command value of clutch hydraulic pressure at the start of sliding of the clutch is detected by the clutch pressure command value detecting means 3 and based on the detected command value, the clutch hydraulic pressure correcting means 5 corrects the clutch hydraulic pressure so as to have a proper value. This arrangement provides the same effect as obtained by the first aspect of the invention and is particularly advantageous in that since the sliding start condition of the clutch is automatically detected by the clutch sliding start detecting means 3, variations attributable to different adjusters can be avoided so that anybody can make an adjustment with ease.
Preferably, the apparatus of the second aspect of the invention is modified such that the clutch hydraulic pressure correcting means 5 corrects the clutch hydraulic pressure based on the difference between a reference clutch pressure command value corresponding to a specified tractive force of the vehicle and the clutch pressure command value detected by the clutch pressure command value detecting means 4 (a third aspect of the invention). With this arrangement, a proper clutch hydraulic pressure command value can be determined based on the tractive force so that a clutch hydraulic pressure closer to the hydraulic pressure at the time of clutch sliding can be effectively obtained, without being affected by variations in other parts (e.g., engine and power line) than the steering section.
Preferably, the apparatus of the second aspect of the invention is modified as follows: the clutch sliding start detecting means 3 is a transmission output-side rotation sensor for detecting the rotation of the output-side of the transmission of the vehicle, and the adjustment mode setting means sets the adjustment mode such that the clutch to be unadjusted is disengaged at all times, when each brake is constantly actuated and the electrical power-assisted steering lever has been shifted to the side of the clutch to be adjusted (a fourth aspect of the invention). With this arrangement, the hydraulic pressure at the start of sliding of the clutch can be easily and accurately detected. In addition, since the clutch to be unadjusted is in its disengaged state at all times, the vehicle does not move during the sliding of the clutch being adjusted.
The apparatus according to the second aspect of the invention may be modified such that the clutch hydraulic pressure changing means provides a step-wise increase in a specified amount in the clutch hydraulic pressure at specified time intervals, starting from a preset initial value (a fifth aspect of the invention). With this arrangement, a clutch hydraulic pressure command value at the start of sliding of the clutch can be readily and accurately obtained.
It is preferable to modify the fourth aspect of the invention such that the clutch hydraulic pressure correcting means 5 corrects the clutch hydraulic pressure based on the difference between a reference clutch pressure command value corresponding to a specified tractive force of the vehicle and the clutch pressure command value detected by the clutch pressure command value detecting means 4 (a sixth aspect of the invention).
The fifth aspect of the invention is preferably modified such that the clutch hydraulic pressure correcting means 5 corrects the clutch hydraulic pressure based on the difference between a reference clutch pressure command value corresponding to a specified tractive force of the vehicle and the clutch pressure command value detected by the clutch pressure command value detecting means 4 (a seventh aspect of the invention).